The present invention relates to an exhaust gas cleaning device for collecting particulates within exhaust gases discharged from an internal combustion engine of an automobile or the like, and cleaning exhaust gases by burning off the collected particulates by means of a heater member.
Particulates collecting devices provided with a filter member made of a ceramic honeycomb structure or a ceramic foamed body, have been proposed for collecting particulates such as carbon particles contained within exhaust gases. In these devices, the flowing resistance of the filter member increases as the particulates accumulate the filter member to reduce the output of an engine. In addition, the accumulated particulates fall from the filter member to reduce the filtering efficiency thereof.
Therefore, it is required to regenerate the filter member by periodically removing the particulates from the filter member.
As the filter member regenerating means, it has been proposed to mount a heater on the filter member for heating the collected particulates to be burnt off. However, in this device, since the exhaust gas temperature is lower than the ignition point of carbon particulates under the normal driving condition of an automobile, the heater is cooled by the exhaust gases so that the particulates are obstructed from being ignited or the flame is blown out by the exhaust gas flow.
In order to improve the ignitability of the collected particulates and in order to prevent the ignited particulates from being blown out, it has been proposed to divide an exhaust gas passage communicated with the engine into two divergent passages and to provide a filter member in each of two divergent passages and a diverter valve on the upstream side or the downstream side of the filter members. By this device having the above structure, exhaust gases are selectively introduced into one of two passages while the filter member of the other passage is heated to burn off the collected particulates.
However, while one of two divergent passages of this device is closed, pressure loss in the filter member of the other divergent passage increases and the flowing speed of the exhaust gases also increases.
The increase in pressure loss makes the durability worse and reduces the output of the engine.
And due to the increase in flowing speed, the particulates collected by the filter member are apt to be blown off when the valve is changed. As a result, the filtering efficiency is reduced.
The above described problem can be overcome by providing a large sized filter member in each of the divergent passages.
However, this device requires two large casings for accommodating such large sized filter members so that the device becomes large.
In addition, while the particulates collected by one of the filter members are heated by the heater, the exhaust gases are not supplied thereto so that a sufficient amount of oxygen is not supplied to the filter member. Therefore, all of the collected particulates cannot be burnt off.
Accordingly, one object of the present invention is to provide an exhaust particulates cleaning device for an engine, having a single filter element and a heater for burning off the particulates collected by the filter member, of which the construction is simple and filter regenerability is excellent.
Another object of the present invention is to provide an exhaust particulates cleaning device for an engine, wherein ignitability and combustibility of collected particulates are improved by controlling the exhaust gas amount supplied to the filter member at the filter member regenerating time.
Still another object of the present invention is to provide an exhaust particulates cleaning device having a means for controlling the exhaust gas amount to be supplied to the filter member into the amount required for regenerating the filter member in accordance with the engine driving condition.